2. 外语
  3. A Canadian researcher has discovered that sound travels 【21】______ air more than one-haft kilometer an hour slower than had been

A Canadian researcher has discovered that sound travels 【21】______ air more than one-haft kilometer an hour slower than had been

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问题    A Canadian researcher has discovered that sound travels 【21】______ air more than one-haft kilometer an hour slower than had been believed. The discovery has surprised many engineers and scientists who learned they had been 【22】______ the wrong speed of sound for many years.
   The speed of sound in air had been 【23】______ to be three-hundred-thirty-one-point-two-nine meters a second. But Doctor George Wong found, 【24】______ accident, that the speed of sound is only three-hundred-thirty-one-point-one-three meters a second. That is a difference of about sixteen centimeters a second.
   Doctor Wong is a member of the National Research Council of Canada. He was studying ways to 【25】______ exactly the sound created by microphones. One of his experiments 【26】______ a number he could use to find the speed of sound. He was 【27】______ to learn that the speed of sound was slower than scientists had thought.
   To explain the difference, Doctor Wong spent eighteen months 【28】______ past test research on the speed of sound. He finally found the 【29】______ of the difference. It was a mathematics mistake 【30】______ in Nineteen-Forty-Two by physicist H-C Hardy.
   Doctor Wong’s 【31】______ does not mean a big change for the science of sound. This is 【32】______ Doctor Hardy and Doctor Wong measured the speed of sound for what is called " standard air".
   Standard air exists only 【33】______ thought. It is a way for scientists to agree 【34】______ the same speed of sound. 【35】______ the air around us, standard air always has a temperature of zero degrees Celsius and the same atmospheric pressure 【36】______ the air at sea level. Standard air al ways have same amounts of nitrogen, oxygen, carbon dioxide and 【37】______ gases. And in standard air, the speed of sound does not change.
   The change in the new speed of sound is 【38】______ small to affect the work of most sound scientists and engineers. But scientists say Doctor Wong’s discovery may 【39】______ improve instruments 【40】______ use the speed of sound to measure very short distances.
【40】
选项 A、whose
B、that
C、what
D、the
答案B
解析 这是一个定语从句，that是连接定语从句的关系代词。
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